A negative electrode slurry, a negative electrode sheet, and a battery

Abstract

The application provides a negative electrode slurry, a negative electrode sheet and a battery, and relates to the technical field of lithium ion batteries.The negative electrode slurry comprises a negative electrode active material, a conductive agent, a binder and a dispersing agent.The dispersing agent comprises at least one of dodecyl sulfosuccinate, castor oil sulfates, lauryl sulfate, butyl oleate sulfates, alkyl pyridine salt chloride, polyoxyhexylene alkyl ether, acetylene glycol, dialkyl sulfosuccinate, polycarboxylate, polymethacrylic acid derivative, styrene-maleic anhydride and condensed naphthalene sulfonate.The negative electrode sheet comprising the negative electrode slurry is applied to the battery, so that the energy density and the cycle performance of the battery can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and more specifically, to a negative electrode slurry, a negative electrode sheet, and a battery. Background Technology

[0002] The negative electrode is a key component of a lithium-ion battery, and its performance directly affects the overall electrochemical performance of the battery. The negative electrode consists of a negative current collector and a negative active layer on the surface of the current collector. The negative active layer is formed by coating a negative electrode slurry, which consists of negative active materials, conductive agents, binders, and solvents. Due to the presence of numerous chemical substances and nanoscale particles, the negative electrode slurry exhibits poor stability during processing, resulting in uneven distribution of various substances within the slurry. This uneven distribution of substances on the coated electrode directly affects the battery's energy density and cycle performance. Summary of the Invention

[0003] The main objective of this application is to provide a negative electrode slurry, a negative electrode sheet, and a battery to solve the problem that the poor stability of the negative electrode slurry affects the energy density and cycle performance of the battery in related technologies.

[0004] To achieve the above objectives, according to a first aspect of this application, a negative electrode slurry is provided, comprising a negative electrode active material, a conductive agent, a binder, and a dispersant;

[0005] The dispersant includes at least one of the following: dodecyl sulfosuccinate, castor oil sulfate, lauryl sulfate, butyl oleate sulfate, alkylpyridinium chloride, polyoxyhexene alkyl ether, ethylene glycol ethynylene, dialkyl sulfosuccinate, polycarboxylate, polymethacrylic acid derivative, styrene-maleic anhydride, and condensed naphthalene sulfonate.

[0006] Further, the molecular weight of the alkylpyridinium chloride is 330-350; the dialkyl sulfosuccinate is selected from sodium dialkyl sulfosuccinate; the polycarboxylate is selected from at least one of sodium polyacrylate, polyethyl methacrylate, and calcium polyacrylate; the polymethacrylate derivative is selected from polymethyl methacrylate; the weight-average molecular weight of styrene-maleic anhydride is 10,000-200,000; and the condensed naphthalene sulfonate is selected from sodium condensed naphthalene sulfonate.

[0007] Further, the dispersant includes castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate, wherein the mass ratio of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate is (3-5):(3-5):(1-3).

[0008] Furthermore, the negative electrode slurry comprises, by mass content: 91%–97% negative electrode active material, 2%–5% binder, 0.3%–3% conductive agent, and 0.1%–1.5% dispersant.

[0009] Furthermore, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, graphene, silicon oxide, and silicon carbon; and / or,

[0010] The adhesive includes at least one of styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, and polyimide; and / or,

[0011] The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanofibers, carbon nanotubes, and graphene.

[0012] Preferably, the negative electrode active material includes graphite and silicon carbon, wherein the mass ratio of graphite to silicon carbon is (6-9):(1-4).

[0013] Furthermore, the initial viscosity of the negative electrode slurry is 3000–4500 mPa·s; after the negative electrode slurry is left to stand for 24 hours at 25°C and ambient humidity ≤25%, the viscosity is 5000–9000 mPa·s, and the difference between the solid content of the upper layer and the solid content of the lower layer is <0.3%.

[0014] A second aspect of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer formed from the negative electrode slurry provided in the first aspect.

[0015] Furthermore, the peel force between the negative electrode current collector and the negative electrode active layer is >1.2 N / m.

[0016] Furthermore, the thickness of the negative electrode active layer is 60–100 μm; and / or,

[0017] The compaction density of the negative electrode active layer is 1.4–1.8 mg / cm³. 3 ; and / or,

[0018] The areal density of the negative electrode is 60–300 mg / cm³. 2 .

[0019] A third aspect of this application provides a battery including the negative electrode provided in the second aspect.

[0020] Furthermore, the battery also includes a positive electrode sheet, which includes a positive current collector and a positive active layer containing a positive active material, wherein the positive active material includes at least one of lithium cobalt oxide, lithium-rich manganese, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate.

[0021] By applying the technical solution of this application and introducing a specific dispersant, the negative electrode slurry can maintain a low viscosity change and a uniform solid content distribution even after being left to stand for a long time, effectively avoiding slurry stratification. This indicates that the negative electrode slurry has excellent stability, which is beneficial to improving the rheological properties and coating uniformity of the negative electrode slurry, thereby helping to improve the energy density and cycle performance of the battery. Detailed Implementation

[0022] As described in the background section of this application, the poor stability of existing negative electrode slurries affects the energy density and cycle performance of batteries. To address this problem, a first aspect of this application provides a negative electrode slurry comprising an active material, a conductive agent, a binder, and a dispersant. The dispersant comprises at least one of the following: dodecyl sulfosuccinate, castor oil sulfate, lauryl sulfate, butyl oleate sulfate, alkylpyridinium chloride, polyoxyethylene alkyl ether, ethylene glycol ethynylene, dialkyl sulfosuccinate, polycarboxylate, polymethacrylic acid derivative, styrene-maleic anhydride, and condensed naphthalene sulfonate.

[0023] The negative electrode slurry comprises active materials, conductive agents, binders, and dispersants. Dispersants improve the dispersion of various substances in the negative electrode slurry, ensuring a uniform distribution of components after 24 hours of standing under specific conditions. First, the uniform distribution of active materials in the slurry provides a more consistent electrochemical reaction environment, ensuring stable battery performance during charge and discharge, and contributing to improved energy density and cycle performance. Second, the distribution of conductive agents in the slurry directly affects the formation of the conductive network within the battery electrode. Good slurry uniformity and stability allow for uniform dispersion of the conductive agent, facilitating the formation of a continuous and stable conductive network and improving electrode conductivity. Good conductivity means smoother electron transport within the battery, higher charge and discharge efficiency, and improved power performance and energy density. Furthermore, the binder adheres the active materials and conductive agents to the negative electrode current collector while maintaining electrode structural stability, preventing cracks or detachment during charge and discharge, which could affect battery cycle life and safety.

[0024] This application utilizes specific dispersants to ensure uniform distribution of components in the negative electrode slurry, thereby maintaining stable viscosity and solid content, enhancing the uniformity and stability of the negative electrode slurry, and thus contributing to improved energy density and cycle performance.

[0025] In some embodiments, the molecular weight of the alkylpyridinium chloride is 330-350; the dialkyl sulfosuccinate is selected from sodium dialkyl sulfosuccinate; the polycarboxylate is selected from at least one of sodium polyacrylate, polyethyl methacrylate, and calcium polyacrylate; the polymethacrylate derivative is selected from polymethyl methacrylate; the weight-average molecular weight of styrene-maleic anhydride is 10,000-200,000; and the condensed naphthalene sulfonate is selected from sodium condensed naphthalene sulfonate.

[0026] In some embodiments, the dispersant comprises castor oil sulfate, styrene-maleic anhydride, and dodecyl sulfosuccinate, wherein the mass ratio of castor oil sulfate, styrene-maleic anhydride, and dodecyl sulfosuccinate is (3-5):(3-5):(1-3). By limiting the dispersant to include castor oil sulfate, styrene-maleic anhydride, and dodecyl sulfosuccinate, the combined use of these three substances can achieve a synergistic effect and improve battery performance.

[0027] Specifically, castor oil sulfate is a natural surfactant with excellent wetting and dispersing properties. Castor oil sulfate can improve the wettability of the negative electrode material, thereby increasing the battery's conductivity and charge / discharge performance. Furthermore, castor oil sulfate exhibits excellent biodegradability and is environmentally friendly.

[0028] Styrene-maleic anhydride is a synthetic polymer material, specifically a copolymer of styrene and maleic anhydride (maleic anhydride) in a copolymerization ratio (molar ratio of styrene to maleic anhydride) of (1–4):1. Styrene-maleic anhydride exhibits good adhesion and stability. It can improve the structural stability of the negative electrode, reducing volume expansion and contraction during charge and discharge, thereby extending battery life. Furthermore, the adhesive properties of styrene-maleic anhydride contribute to improving the mechanical stability of the battery.

[0029] Dodecyl sulfosuccinate is a surfactant with good dispersibility and stability. It can improve the dispersibility of negative electrode materials, reduce particle agglomeration, and thus improve the charge-discharge efficiency of the battery. Furthermore, dodecyl sulfosuccinate can also improve the cycle stability and thermal stability of the battery.

[0030] When these three substances are used together, their advantages complement each other: the wettability and dispersibility of castor oil sulfate and dodecyl sulfosuccinate can improve the conductivity of the negative electrode active layer; the bonding properties of styrene-maleic anhydride can improve the structural stability of the battery and reduce volume changes; dodecyl sulfosuccinate can improve the cycle stability of the battery and reduce the risk of thermal runaway; and the biodegradability of castor oil sulfate makes the entire formulation more environmentally friendly.

[0031] Therefore, this application uses castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a specific ratio as dispersants for the negative electrode slurry. The combined use of these three substances can improve the energy density and cycle performance of the battery.

[0032] This application does not limit the content of each component in the negative electrode slurry, and can be adjusted according to actual needs. In some embodiments, the negative electrode slurry comprises, by mass content: 91% to 97% negative electrode active material, 2% to 5% binder, 0.3% to 3% conductive agent, and 0.1% to 1.5% dispersant. By limiting the proportion of each substance in the negative electrode active layer, energy density and cycle performance can be further improved.

[0033] The negative electrode active material layer contains 91% to 97% by mass, for example, 91%, 95%, 96%, 97%, or any combination thereof; the binder in the negative electrode active material layer contains 2% to 5% by mass, for example, 2%, 3%, 4%, 5%, or any combination thereof; the conductive agent in the negative electrode active material layer contains 0.3% to 3% by mass, for example, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination thereof; and the dispersant in the negative electrode active material layer contains 0.1% to 1.5% by mass, for example, 0.1%, 0.2%, 0.5%, 1%, 1.5%, or any combination thereof.

[0034] This invention does not limit the specific types of negative electrode active material, binder, and conductive agent. For example, in some embodiments, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, graphene, silicon oxide, and silicon carbon; and / or, the binder includes at least one of styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, and polyimide; and / or, the conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanofibers, carbon nanotubes, and graphene.

[0035] In some embodiments, the negative electrode active material includes graphite and silicon carbon. By mixing graphite and silicon carbon in a specific ratio, the specific capacity of the negative electrode can be significantly improved while ensuring a certain degree of cycle stability, thereby increasing the energy density of the entire battery. The stability of graphite can also be used to mitigate the effect of silicon volume expansion and improve the cycle stability of the composite material. In addition, it can improve the overall conductive network of the negative electrode material, which helps to improve the rate performance of the battery, that is, the ability to charge and discharge quickly.

[0036] In some embodiments, the mass ratio of graphite to silicon-carbon is (6-9):(1-4). By limiting the mass ratio of graphite to silicon-carbon to (6-9):(1-4), the energy density of the battery can be significantly improved while maintaining a certain level of cycle stability and safety. Through appropriate compounding, the high capacity advantage of silicon is utilized, while the stability and conductivity of graphite are leveraged, achieving a balance between performance and stability.

[0037] The mass ratio of graphite to silicon carbon is (6-9):(1-4), for example, 6:4, 7:3, 8:2, 9:1 or any combination thereof.

[0038] In some embodiments, the initial viscosity of the negative electrode slurry is 3000-4500 mPa·s. After the negative electrode slurry is left to stand for 24 hours at 25°C and ambient humidity ≤25%, the viscosity is 5000-9000 mPa·s, and the difference between the solid content of the upper layer and the solid content of the lower layer is <0.3%.

[0039] The viscosity of the negative electrode slurry directly affects its coating performance, leveling properties, and the uniformity of the final negative electrode. Viscosity can be understood as the slurry's viscosity, and its magnitude is one of the indicators of slurry stability. A lower viscosity value indicates that the negative electrode slurry has better fluidity, which helps to achieve a more uniform coating during the coating process and reduces coating defects such as dark spots, particle unevenness, or foil wrinkles and scratches. At the same time, the slurry's viscosity changes less, remaining stable over a longer period, which is beneficial for control and operation during the production process.

[0040] This application limits the viscosity of the negative electrode slurry to 5000-9000 after standing for 24 hours at 25°C and ambient humidity ≤25%, with the unit being "millipascal-seconds" (mPa·s). This indicates that the negative electrode slurry has a low viscosity value and the viscosity change of the negative electrode slurry is small. This application can effectively control the viscosity of the slurry, optimize the stability and processability of the slurry, and thus improve the performance and production efficiency of the battery.

[0041] The difference in solid content between the upper and lower layers is used to characterize the sedimentation stability of the negative electrode slurry after 24 hours of settling, and can be used to evaluate the dispersion uniformity and stability of the slurry. Specifically, sedimentation stability is a performance indicator that measures whether the active material particles are evenly distributed after the slurry has been settling, and whether there is significant sedimentation or floating. After a long period of settling, the smaller the difference in solid content between the upper and lower layers, the more uniform the particle dispersion in the slurry, which can ensure the uniformity of subsequent coating processes and the consistency of battery performance. If the difference in solid content between the upper and lower layers is large, it indicates that the slurry has undergone a certain degree of sedimentation after 24 hours of settling, resulting in a difference in solid content between the upper and lower layers, which may affect the uniformity of coating and the final performance of the battery.

[0042] This application specifies that after the negative electrode slurry is left to stand for 24 hours at 25°C and ambient humidity ≤25%, the difference between the solid content of the upper layer and the solid content of the lower layer is <0.3%. This indicates that after 24 hours of standing, the solid content ratio of the upper layer to the lower layer of the slurry is very close, almost identical. This means that the sedimentation stability of the slurry is very good, the particles are evenly distributed in the slurry, and there is no obvious sedimentation or floating phenomenon. This is beneficial to ensuring the long-term stability of the slurry, the uniformity of the coating process, and the performance consistency of the final battery electrode.

[0043] Therefore, this application limits the viscosity of the negative electrode slurry to 5000-9000 mPa·s after standing for 24 hours at 25°C and ambient humidity ≤25%, and the difference between the solid content of the upper and lower layers is <0.3%. This allows the negative electrode slurry to maintain low viscosity change and uniform solid content distribution even after long-term standing. The components in the negative electrode slurry can maintain a uniform distribution, effectively avoiding slurry stratification and ensuring excellent stability. This improves the rheological properties and coating uniformity of the negative electrode slurry. The uniform distribution of substances on the coated negative electrode helps to improve the energy density and cycle performance of the battery, ensuring stable battery performance during charging and discharging.

[0044] Furthermore, the rheological properties of the negative electrode slurry are crucial to the coating process. Good uniformity and stability of the slurry mean more controllable rheological properties, ensuring that the slurry can be evenly spread on the current collector during high-speed coating, forming an electrode layer of consistent thickness. The uniformity and stability of the slurry also affect the process control and production efficiency of battery manufacturing. By ensuring that the negative electrode slurry meets the above requirements, the slurry utilization rate in the battery manufacturing process and the consistency of battery quality and performance are improved.

[0045] A second aspect of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer formed from the negative electrode slurry provided in the first aspect.

[0046] The peel force between the negative electrode current collector and the negative electrode active layer reflects the strength of their adhesion. If the peel force is too low, it means that the adhesion between the negative electrode current collector and the negative electrode active layer is not strong, and active material may fall off during the charging and discharging process, affecting the battery's performance and lifespan.

[0047] In some embodiments, the peel force between the negative electrode current collector and the negative electrode active layer is >1.2 N / m.

[0048] This application specifies that the peel force between the negative electrode current collector and the negative electrode active layer is >1.2 N / m, indicating that the adhesion between the negative electrode current collector and the negative electrode active layer is strong. This means that there is good adhesion between the negative electrode current collector and the negative electrode active layer, and the electrode can maintain structural stability during battery charge and discharge cycles, reducing the risk of internal short circuits and extending the battery's service life.

[0049] In the specific implementation of this application, the peel force test method can be a 180° peel test, also known as an adhesive tape peel test. Specifically, a sample of a negative electrode sheet that has been coated and dried is selected, and a strip of width (e.g., 10 mm) is cut at one end of the sample for adhesive tape. This strip should be perpendicular to the edge of the current collector. A piece of standard adhesive tape (e.g., 3M test tape) is pasted onto the cut surface of the negative electrode active layer, ensuring that the tape is completely bonded and free of air bubbles. The end of the sample with the adhesive tape is fixed to a peel force testing instrument. The instrument pulls the tape off the negative electrode active layer at a 180° angle and a constant tensile speed (e.g., 200 mm / min), and measures the force required during the peeling process. The testing instrument records the average force required during the peeling process, which is the peel force.

[0050] The negative electrode current collector has two opposing functional surfaces for coating negative electrode slurry to form a negative electrode active layer. Both surfaces of the negative electrode current collector are provided with a negative electrode active layer. In some embodiments, the thickness of the negative electrode active layer is 60–100 μm. Here, the thickness of the negative electrode active layer refers to the sum of the thicknesses of the negative electrode active layers on the two functional surfaces of the negative electrode current collector.

[0051] In some embodiments, the compaction density of the negative electrode active layer is 1.4–1.8 mg / cm³. 3 Compacted density refers to the mass of active material that can be contained within a unit volume. By limiting the compacted density of the negative electrode active layer within the aforementioned range, the active material can be packed more tightly, which helps to achieve higher capacity.

[0052] In some embodiments, the areal density of the negative electrode is 60–300 mg / cm³. 2 Areal density refers to the mass of the active material coated on both sides of the negative electrode per unit area. By limiting the areal density of the negative electrode to the above range, it is possible to ensure that the energy density of the battery is high enough, optimize the lithium-ion transport path and electronic conductivity, and also help control the expansion of the battery during charging and discharging, reduce stress accumulation during cycling, and thus improve the cycle stability of the battery.

[0053] In the specific preparation of the negative electrode sheet, the negative electrode active material, conductive agent, binder, and dispersant can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained. The negative electrode current collector can be made of at least one of copper foil, nickel foam, and copper foam.

[0054] A third aspect of this application provides a battery including the negative electrode provided in the second aspect.

[0055] Because it includes the aforementioned negative electrode, this battery not only has high energy density and excellent cycle performance, but also excellent charge and discharge performance at high rates.

[0056] In some embodiments, the battery further includes a positive electrode sheet, which includes a positive current collector and a positive active layer containing a positive active material.

[0057] The positive electrode sheet includes a positive current collector and a positive active layer disposed on the surface of the positive current collector. The positive active layer includes a positive active material, a second conductive agent, and a second binder.

[0058] In the specific preparation of the positive electrode sheet, the positive electrode active material, the second conductive agent, and the second binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70%–99% of the positive electrode active material, 0.5%–15% of the second conductive agent, and 0.5%–15% of the second binder.

[0059] The positive current collector can be made of at least one of aluminum foil and nickel foil; the second conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the second binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0060] This application does not limit the specific type of positive electrode active material in the positive electrode sheet, and can be a positive electrode active material commonly used in batteries, such as a composite oxide of lithium with at least one of cobalt, nickel, manganese, or combinations thereof. Specifically, the positive electrode active material includes at least one of lithium cobalt oxide, lithium-rich manganese, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate.

[0061] The battery also includes a separator. This application does not limit the specific choice of separator material, and it can be separator materials commonly used in batteries, such as polypropylene separators, polyethylene separators, polypropylene / polyethylene double-layer composite separators, polypropylene / polyethylene / polypropylene (PP / PE / PP) triple-layer composite separators, etc.

[0062] In battery manufacturing, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to obtain battery cells. The battery cells are then encapsulated in pre-stamped aluminum-plastic films. After the encapsulated batteries are dried, electrolyte is injected into the dried batteries. The batteries are then aged, formed, and resealed to complete the battery manufacturing process.

[0063] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0064] Example 1

[0065] The method for preparing the negative electrode sheet in this embodiment includes:

[0066] A negative electrode active material, binder, conductive agent, and dispersant are mixed in a mass ratio of 95%:3.5%:1.0%:0.5%, and 50% water is added to the mixture to form a negative electrode slurry. The negative electrode active material is a mixture of graphite and silicon-carbon in a mass ratio of 9:1; the binder is polyacrylic acid (PAA) and styrene-butadiene rubber (SBR); the conductive agent is conductive carbon black (SP) and carbon nanotubes (CNTs); and the dispersant is castor oil sulfate. The negative electrode slurry is coated onto a 6μm thick copper foil current collector, with a double-sided coating areal density of 110 g / m². 2 After cold pressing and vacuum drying, a negative electrode sheet with a thickness of 77μm is obtained.

[0067] Example 2

[0068] The difference from Example 1 is that the dispersant is styrene-maleic anhydride.

[0069] Example 3

[0070] The difference from Example 1 is that the dispersant is dodecyl sulfosuccinate.

[0071] Example 4

[0072] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 4:4:2.

[0073] Example 5

[0074] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 3:5:2.

[0075] Example 6

[0076] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 5:3:2.

[0077] Example 7

[0078] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 5:4:1.

[0079] Example 8

[0080] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate, styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 3:4:3.

[0081] Example 9

[0082] The difference from Example 1 is that the dispersant is a mixture of castor oil sulfate and styrene-maleic anhydride in a mass ratio of 1:1.

[0083] Example 10

[0084] The difference from Example 1 is that the dispersant is a compound of castor oil sulfate and dodecyl sulfosuccinate in a mass ratio of 2:1.

[0085] Example 11

[0086] The difference from Example 1 is that the dispersant is a compound of styrene-maleic anhydride and dodecyl sulfosuccinate in a mass ratio of 2:1.

[0087] Example 12

[0088] The difference from Example 1 is that the dispersant is polyoxyhexene alkyl ether.

[0089] Example 13

[0090] The difference from Example 1 is that the mass ratio of graphite to silicon carbon is 8:2.

[0091] Example 14

[0092] The difference from Example 1 is that the mass ratio of graphite to silicon carbon is 6:4.

[0093] Example 15

[0094] The difference from Example 1 is that the negative electrode active material is graphite.

[0095] Example 16

[0096] The difference from Example 1 is that the negative electrode active material is silicon carbon.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that no dispersant is added to the negative electrode active layer, and the mass ratio of negative electrode active material, binder and conductive agent is 95.5%:3.5%:1.0%.

[0099] Test case

[0100] I. Performance Testing of Negative Electrode Slurry

[0101] 1. Viscosity

[0102] The negative electrode slurry was placed in a test cup, and the initial viscosity and the viscosity after standing for 24 hours were tested using a rotational viscometer.

[0103] 2. Test of the difference in solid content between the upper and lower layers

[0104] After standing for 24 hours, use a pipette to take the top 3mm of the negative electrode slurry and place it on an empty foil to weigh m0. Bake it for 1 minute and weigh it m1. The rate of change of the difference between the two is recorded as the upper solid content, i.e., upper solid content = (m0-m1) / m0×100%.

[0105] Use a pipette to take a 3mm sample of the lower layer of the negative electrode slurry and place it on an empty foil. Weigh it (m2). Bake it for 1 minute and weigh it (m3). Record the rate of change of the difference between the two as the lower layer solid content, i.e., lower layer solid content = (m2-m3) / m2×100%.

[0106] II. Negative Electrode Performance Testing

[0107] Negative electrode peel strength test: The peel strength is quantitatively determined using the 180° peel method. The free end of the negative electrode is folded 180°, and the free end of the electrode and the test plate are clamped on the upper and lower clamps respectively. In the same environment, a tensile testing machine is used to continuously peel the electrode until the copper foil current collector and the negative electrode active layer are completely separated. The peel strength value is then read, which is the electrode peel strength.

[0108] III. Electrochemical Performance Testing

[0109] 1. Cyclic stability test

[0110] Large single-crystal lithium nickel cobalt manganese oxide (NCM523) was mixed with conductive carbon black and PVDF at a mass ratio of 94:3.0:3.0 and dissolved in N-methylpyrrolidone, with the solid content controlled at 50%, to obtain a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil current collector, and after vacuum drying at 95°C, rolling, and pressurizing, a positive electrode sheet was obtained.

[0111] The negative electrode, separator, and positive electrode of the examples and comparative examples were assembled into a lithium-ion battery and injected with electrolyte to obtain a soft-pack battery with a capacity of about 400mAh. The electrolyte was 1mol / L LiPF6 / ethylene carbonate (EC) + propylene carbonate (PC) + diethyl carbonate (DEC) + EMC (volume ratio 1:0.3:1:1), and the separator was a PP / PE / PP three-layer composite separator.

[0112] The aforementioned pouch cell was used to test the cycle performance of the material. It was charged at a constant current rate of 3C to 4.20V, then charged at a constant voltage rate with the current gradually decreasing to 0.05C, and finally discharged at a discharge rate of 1C to 2.75V. This charge-discharge cycle was repeated 400 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q400 at the 400th cycle were measured. The 400-cycle capacity retention rate was calculated as Q400 / Q1 × 100%.

[0113] 2. 2C charging constant current ratio

[0114] The aforementioned pouch battery was charged at 25°C with a constant current of 2C to 4.20V, followed by constant voltage charging, with the current gradually decreasing to 0.05C. The charging capacity during the 2C charging stage and the total charging capacity throughout the entire charging process were recorded. The total charging capacity should include the charging capacity during the 2C constant current charging stage and the subsequent constant voltage charging stage.

[0115] The 2C charging constant current ratio can be calculated using the following formula: 2C charging constant current ratio = 2C constant current charging capacity / total charging capacity × 100%.

[0116] 3. Expansion Rate Test

[0117] The initial cell thickness d1 in the test example and comparative example. The above battery was charged at 25°C with a constant current of 3C to 4.50V, then charged at a constant voltage of 0.05C to 4.50V, and then discharged at a discharge rate of 1C to 3.0V. This charge-discharge cycle was repeated 400 times, and the cell thickness d2 after 400 cycles was measured. The expansion rate was calculated according to the expansion rate = (d2-d1) / d1×100%.

[0118] 4. Energy density

[0119] Using a battery charge / discharge tester, the battery was charged at 25°C with a constant current of 0.5C to 4.25V, then charged with a constant voltage until the current dropped to 0.02C. After resting for 5 minutes, the battery was discharged at a constant current of 0.5C to 2.5V, and the initial discharge capacity Q of the battery was recorded. 放 and the first discharge energy E 放 The volume of the battery cell is denoted as V, and the battery energy density (Wh / L) = E. 放 / V.

[0120] The test results are shown in Tables 1 and 2.

[0121] Table 1

[0122]

[0123]

[0124] Table 2

[0125]

[0126] As shown in Tables 1 and 2, the addition of dispersant effectively reduces slurry viscosity, slows down viscosity changes, reduces settling velocity, and improves slurry flowability, resulting in better leveling properties in the coating. Furthermore, the addition of dispersant does not significantly affect the charging constant current ratio or cycle performance of the lithium battery, but it effectively improves the processing performance of the anode, enhances the uniformity and stability of the negative electrode slurry, and simultaneously increases the energy density of the lithium-ion battery.

[0127] Specifically, the viscosity of the negative electrode slurry in Examples 1-16 fluctuates little. After standing for 24 hours, the difference between the solid content of the upper layer and the lower layer is <0.3%, and further ≤0.25%. The electrode peeling force is ≥1.5N / m. When applied to batteries, the energy density of the battery is ≥620Wh / L, the constant current ratio of 2C charging is ≥74.4%, the capacity retention rate of 400T 3C / 1C cycle is ≥85.6%, and the expansion rate of 400T 3C / 1C cycle is ≤10.5%.

[0128] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode slurry, characterized by, The negative electrode slurry comprises a negative electrode active material, a conductive agent, a binder, and a dispersant. The dispersant comprises castor oil sulfate, styrene-maleic anhydride, and dodecyl sulfosuccinate, and the mass ratio of the castor oil sulfate, the styrene-maleic anhydride, and the dodecyl sulfosuccinate is (3-5):(3-5):(1-3). The negative electrode active material comprises graphite and silicon-carbon, and the mass ratio of the graphite and the silicon-carbon is (6-9):(1-4).

2. The negative electrode slurry of claim 1, wherein The molecular weight of the styrene-maleic anhydride is 10,000-20,000.

3. The negative electrode slurry of claim 1, wherein The negative electrode slurry comprises, in terms of mass content, 91-97% of the negative electrode active material, 2-5% of the binder, 0.3-3% of the conductive agent, and 0.1-1.5% of the dispersant.

4. The negative electrode slurry of any one of claims 1-3, wherein The binder comprises at least one of styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, polyvinylidene fluoride, polyacrylonitrile, polytetrafluoroethylene, and polyimide; and / or The conductive agent comprises at least one of conductive carbon black, conductive graphite, nanocarbon fiber, carbon nanotube, and graphene.

5. The negative electrode slurry according to any one of claims 1 to 3, wherein The initial viscosity of the negative electrode slurry is 3,000-4,500 mPa·s, and after the negative electrode slurry is left to stand at 25°C under an ambient humidity of ≤25% for 24 hours, the viscosity is 5,000-9,000 mPa·s, the difference between the solid content of the upper layer and the solid content of the lower layer is <0.3%.

6. A negative electrode sheet characterized by The battery further comprises a positive electrode sheet comprising a positive electrode current collector and a positive electrode active layer comprising a positive electrode active material, the positive electrode active material comprising at least one of lithium cobaltate, lithium-rich manganese, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate.

7. The negative electrode sheet according to claim 6, characterized by The peeling force between the negative electrode current collector and the negative electrode active layer is >1.2 N / m.

8. The negative electrode sheet according to claim 6 or 7, characterized in that, The thickness of the negative electrode active layer is 60-100 μm; and / or The compaction density of the negative electrode active layer is 1.4 to 1.8 mg / cm 3 ; and / or, The face density of the negative electrode sheet is 60 to 300 mg / cm 2 .

9. A battery, characterized by The battery further comprises a positive electrode sheet comprising a positive electrode current collector and a positive electrode active layer comprising a positive electrode active material, the positive electrode active material comprising at least one of lithium cobaltate, lithium-rich manganese, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate.

10. The battery of claim 9, wherein, ​

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